The present invention relates to compositions of matter containing the uranyl ion. More specifically, the present invention relates to such compositions of matter which are highly useful in uranium isotope separation processes.
Over the past few years, a significant search has been made for the discovery of volatile uranyl compounds which can be used for the separation of isotopes. Such a process and compounds useful therein are disclosed in copending application Ser. No. 865,963 filed on Dec. 30, 1977 in the names of Martin B. Dines, et al., and a number of specific compounds useful in that process are similarly disclosed in U.S. patent application Ser. No. 868,450 filed on Jan. 10, 1978 in the names of Richard B. Hall et al. now abandoned. The principal compounds disclosed in those applications have the general formula UO.sub.2 (1,1,1,5,5,5 hexafluoro-2,4-pentanedionate).sub.2.L, where L is a neutral ligand such as tetrahydrofuran and others, such as ethanol or N,N-dimethylformamide which are listed in those patent applications. In a subsequent application given Ser. No. 961,363 and filed on Nov. 16, 1978, now U.S. Pat. No. 4,243,597, Messrs. Hall et al. disclose compounds having the general formula UO.sub.2 AA'L.sub.n where n is 0 or 1, A and A' are anions whose conjugate acids have boiling points less than about 200.degree. C. and pK.sub.a values of 4.8 or less, and where L is a neutral ligand having a boiling point less than about 190.degree. C. and an equilibrium constant for its exchange reaction with the complexed tetrahydrofuran of between about 10.sup.-3 and 10.sup.3.
All of these compounds have been found to be particularly useful in such isotope separation processes precisely because they are relatively volatile uranyl ion-containing compounds, and they also have isotopically shifted infrared absorption spectra associated therewith. Therefore, by irradiating these compounds in the vapor phase with infrared radiation which is preferentially absorbed by molecular vibrations of molecules containing a predetermined isotope of the element which is to be separated, excited molecules enriched in that isotope can be separated therefrom. In particular, the compounds disclosed are highly significant in that they possess infrared absorptions which exhibit isotopic shifts within the range of the wavelength of commercially available CO.sub.2 lasers.
In the background section of U.S. patent application Ser. No. 865,963, a number of references teaching various compounds having the general formula UO.sub.2 (.beta.-diketonate).sub.2.L where L is a neutral ligand, are disclosed. These include U.S. patent application Ser. No. 662,600 of Messrs. Schlessinger and Brown published in the Official Gazette on Mar. 6, 1951, Chemical Abstracts, 46, 10192b, as well as those same authors' subsequent publication in the Journal of the American Chemical Society, 75, pages 2446-8 (1953) in which they disclose UO.sub.2 (1,1,1-trifluoro-2,4-pentanedionate).sub.2 having the highest vapor pressure for any of the uranyl .beta.-diketonates which they studied, namely about 0.0027 torr at 130.degree. C.
In the aforesaid application of Messrs. Dines et al., reference is also made to a comprehensive review of the properties of various uranyl compounds with chelating ligands, namely Casellato et al., in Inorganica Chemica Acta, 18, 77-112 (1976). In that article the behavior of the actinides in their various oxidation states and combined with various organic chelating ligands such as the .beta.-diketones, is discussed in detail. The majority of the anions disclosed in that article, however, have conjugate acids which have pK.sub.a values considerably higher than 4.8. These include disclosures of compounds of the general formula UO.sub.2 (A).sub.2.L, where A is tropolonate, acetylacetonate, and the amine of dibenzoylmethane, thenoyltrifluoroacetone, benzoylacetone, trifluoroacetone, etc.
Reference is also made in the Dines et al. application to Subramanian et al., "Complexes of Uranyl .beta.-Diketones with Aromatic Amine N-Oxides," Journal of Inorganic Nuclear Chemistry, 33, 3001 (1971) which discusses a number of compounds of the general formula UO.sub.2 (1,1,1,5,5,5,-hexafluoroacetylacetonate).sub.2 L, where the ligands, L, are various amine N-oxides, such as pyridine N-oxide. It is also noted that the same types of compounds, but where L is a sulfoxide, such as dibutyl sulfoxide, or a phosphine oxide, are disclosed in articles such as Sieck, "Gas Chromatography of Mixed-Ligand Complexes of the Lanthanides and Related Elements" submitted for his Ph.D. thesis, Iowa State University, 1971 and two other articles by Sieck in Chemical Abstracts, 75, 147395Q and Nuclear Science Abstracts, 25, (17), 39410 (1971). Also Mitchell (Synergic Solvent Extraction and Thermal Studies of Fluorinated Beta-Diketone-Organophosphorous Adduct Complexes of Lanthanide and Related Elements, Ph.D. Thesis, Iowa State University, 1970) prepared the tributylphosphate complex of UO.sub.2 (hfacac).sub.2, where (hfacac) is the 1,1,1,5,5,5 hexafluoro-2,4-pentanedionate anion, and showed that it vaporized at about 150.degree. C.
In co-pending application, Ser. No. 961,363, now U.S. Pat. No. 4,243,597, Messrs. Hall, Kaldor, Kramer and Dines disclose a number of volatile uranyl compounds, including those having the general formula UO.sub.2 AA'L.sub.n, where A and A' are certain selected anions and L is again a neutral ligand. Both of the above-noted co-pending applications of Messrs. Dines et al. and Hall et al. discuss an article by Belford et al. (J. Inorg.Nucl.Chem. 14 169 (1960)) in which the authors describe their preparation of UO.sub.2 (hfacac).sub.2.4H.sub.2 O, which they describe as decomposing upon heating above 58.degree. C. This article then goes on to discuss the infrared absorption bands for various uranyl compounds, and the effect of ligand substitution on the visible spectra, concluding that the more basic ligands attach more securely to the uranium atom, thus decreasing its coordinating tendencies.
A number of references have also discussed compounds variously described as uranyl phthalocyanine (Bloor et al., Canadian Journal of Chemistry, 42, 2201-2208 (1964)), said to be sublimable under a vacuum "below 0.01 mm pressure at 400.degree.-450.degree. C." and uranyl superphthalocyanine (Day, Marks and Wachter, "Large Metal Ion-Centered Template Reactions. A Uranyl Complex of Cyclopentakis (2-iminoisoindoline)": J.A.C.S., 97:16, Aug. 6, 1975, 4519-4527). Furthermore, U.S. Pat. No. 4,097,384 to Messrs. Coleman and Marks discloses the possible laser irradiation of that compound, as well as other possible uranyl compounds. The Day, Marks and Wachter paper was presented orally at the American Crystallographic Association meeting in Berkeley, Calif. in March of 1974, as well as at the American Chemical Society meeting in Los Angeles in April of 1974. In a later paper entitled "Large Metal Ion-Centered Template Reactions. Chemical and Spectral Studies of `Superphthalocyanine` Dioxocyclopentakis (1-iminoisoindolinato) Uranium (VI) and Its Derivatives," Messrs. Marks and Stojakovic, J. Amer. Chem. Soc., 100, page 1695 (March 1978), further discuss this compound and indicate that a product can be obtained by sublimation at 400.degree. C.
In an article entitled "Volatile Complexes of Some Lanthanides and Related Elements with Fluorinated Beta-Diketones and Organophosphorous Adducts," Anal. Chim. Acta, 57, 415-424 (1971), Mitchell et al. discuss the use of various bases to displace the water of hydration from chelates of the lanthanides with trifluoroacetylacetone and hexafluoroacetylacetone. They thus employ tri-n-butyl phosphate in compounds having the general formula M(A).sub.3.2TBP, M being one of a number of lanthanide elements. They note that these compounds were considerably more volatile and thermally stable than the corresponding hydrated chelates and conclude that the " . . . water of hydration is instrumental in the thermal degradation of chelates of the rare earths with .beta.-diketones."
In a series of articles by Levy et al. and Taylor et al., J.C.S. Dalton, 1628-1640 (1977) the authors discuss their studies of UO.sub.2 (hexafluoropentane-2,4-dionato).sub.2 (trimethylphosphate). The final articles in this series discuss the structure of the polymorphs of this compound.
Finally, in an article by Messrs. Johnson, Taylor and Waugh, J. Inorg. Nucl. Chem., Vol. 41, pages 827-831 (1979) the authors discuss the compound UO.sub.2 (hfacac).sub.2 NH.sub.3.